I recently installed the "Slendide Ariston" stackables and needed to purchase separately from the vendor, the 1. Stacking kit, 2. Venting kit. and 3. the Drain pan. I purchased the rest of the hardware from Home Depot. FYI, there is a very good post on this forum complete with color photos of an install of a combination unit. The prep work is the same for the stackables. Good Luck and don't get in a hurry.